package day03;

import java.util.Scanner;

public class Extend {
    public static void main(String[] args) {
        //1.
//        int a=100,b=200;
//        System.out.println("Max:"+(a>b?"a:"+a:"b:"+b));
//        System.out.println();
//        if (a > b) {
//            System.out.println("Max:a="+a);
//        }else{
//            System.out.println("Max:b="+b);
//        }
        //2.
//        int year=new Scanner(System.in).nextInt();
//        if((year%4==0&&year%100!=0)||year%400==0){
//            System.out.println("闰");
//        }else {
//            System.out.println("不闰");
//        }
        //3.
        int grade=new Scanner(System.in).nextInt();
        if (grade<60){
            System.out.println("D");
        }else if (grade<80){
            System.out.println("C");
        }else if (grade<90){
            System.out.println("B");
        }else {
            System.out.println("A");
        }
    }
}
